Gas plating metal deposits comprising boron



Nov. 28, 1967 W. c. JENKIN 3,355,318

GAS PLATING METAL DEPOSITS COMPRISING BORON 2 Sheets-Sheet 1 Filed Sept. 26, 1963 26 lN-SULA T/O/V CHAMBER CAN BE SQUARE OW CIRCULAR Fig. 2

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GAS PLATING METAL DEPOSITS COMPRISING BORON Nov. 28, 1967' 2 Sheets-Sheet 2 Filed Sept. 26, 1963 ak b k0:

MWIQQQ ATTORNEY5 United States Patent 3,355,318 GAS PLATING METAL DEIGSITS COMPRISING BORQN William C. Jenhin, Dayton, (lhio, assignor to Union Carbide Corporation, New York, NY. Filed Sept. 26, 1963, Ser. No. 311,892 3 Claims. (Cl. 117--107.2)

This invention relates to a method of producing metal deposits and coatings of boron and alloys thereof.

t is known to plate metal on substrate surfaces by thermal decomposition of a gaseous metal compound, or metal bearing compounds, which are brought in contact with the heated substrate. Such a process is commonly referred to as gas plating to distinguish from volatilized metal-condensation processes and the like vapor phase metal plating.

The production of metal deposits containing boron, and more particularly hard metal coatings of metal and boron by gas plating has not been known or practiced heretofore. This is the subject matter of the present invention as hereinafter described and claimed.

Boron compounds, for example boron hydrides and particularly diborane, decompose to form hydrogen and boron at temperatures above about 575 F. In the presence of a volatilized carbonyl of a metal, however, it has been discovered that boron hydride decomposes at a much lower temperature, and that boron is co-deposited along with the metal of the metal carbonyl to produce hard or tough wearand heat-resistant coatings.

It has further been discovered by experimental tests that the presence of even small amounts of boron render such metal deposits either tough or hard and resistant to heat and wear. Nickel-boron deposits, for example, are hard. The resultant improved physical properties of metal coating deposits containing boron, insofar as now known, is not due to stress conditions in the metal deposit but appears to result by the formation of a metal alloy or diffusion metal deposit which exhibit distinctly different physical properties than the metals themselves. This is indicated by tests which have shown that the metal deposits produced according to the present invention and containing boron, can be heated to 1200 F. with but a minor decrease in the hardness. On the other hand, metal coatings hardened by physical stresses set up in the deposit do not retain their original hardness when so heated.

The unexpected results obtained by co-deposition of metal deposits which comprise boron, even at low temperatures, e.g. 300 F., is believed to be due to one or more factors or phenomena. Employing admixtures of boron hydrides and metal carbonyls it is theorized that carbon monoxide present in the plating chamber reacts with the boron compound in the presence of metal carbonyls to form a heat-decomposable compound of boron. It is also possible that boron hydride may react with a carbon monoxide molecule of a metal carbonyl to form a new compound which is thermally decomposable at relatively low temperatures, e.g. 300 to 400 F. Diborane and carbon monoxide, for example, react to form a compound having the general formula B H .2O0.

In accordance with the present invention, it has been discovered that co-deposition of metal deposits including boron occurs with metals that form a volatile carbonyl or carbonyl derivative. The metals are found in Groups VI-B, VIIB and VIII of the Periodic Table of Elements. Such metals include nickel, chromium, iron, cobalt, molybdenum, tungsten, platinum, palladium, rhodium, etc.

To produce the boron modified metal deposits, and such as may be referred to as metal alloy deposits, the

3,355,318 Patented Nov. 28, 1967 same preferably is obtained by gas plating using a suitable mixture of such metals whereby co-deposition of the metals takes place. The carbonyl of the metal or metals to be modified or alloyed with boron is converted to a gaseous state, if liquid, by flowing metered amounts of the liquid through a heated coil. The resultant gaseous metal carbonyl may then be mixed with boron hydride vapors and conducted to the plating chamber. The vapors may, if desired, be mixed with other gases such as is common practice in gas plating processes, to control the metal bearing gaseous mixture or modify its composition and metal deposition characteristics.

The gas plating mixture of compounds of boron and other metal or metals is conveyed to the plating chamber while the same is maintained below the temperature at which the metal bearing gases thermally decompose. The substrate or object on which the metal deposit is to be received is disposed in the plating chamber and maintained heated to a temperature such as will cause the metal bearing gaseous mixture to thermally decompose and co-deposit the metal constituents of the metal compounds.

For heating the article or substrate to receive the metal deposit, suitable electrical resistance heating means may be used, as well as high frequency induction current from a coil, or infra-red radiators or the like. The gas plating chamber is provided with an exhaust to remove the waste vapors. Where use is made of solid metal carbonyls, the same are preferably heated in a bed or container and a carrier gas, e.g. carbon monoxide, nitrogen or the like relatively inert gas, is passed thereover or through a bed of the solid particles of metal carbonyl to carry the vapors of the carbonyl to the plating chamber.

In the accompanying drawings there is illustrated a suitable gas plating apparatus for carrying out the gas plating in accordance with this invention.

In the drawings FIGURE 1 is a sectional view taken of a gas plating chamber and illustrating its construction and operation for gas plating substrate surfaces in accordance with this invention;

FIGURE 2 is a similar sectional view taken through a gas plating apparatus useful for gas plating metal deposits using infra-red lamps as a source of heat; and

FIGURE 3 is a sectional view of modified apparatus for gas plating hollow patterns and the like shapes.

Referring to the drawings in detail and FIGURE 1 in particular, reference character 10 designates a gas plating chamber having bottom wall 11 and side walls 12 and 13 with a lid or cover 14. The latter is removably secured to the top or side walls and sealed there by a gasket 16 to provide a closed plating chamber. Inlet conduit means 17 and 18 is provided for introducing the metal bearing gases. An exhaust outlet is arranged in the lid or cover, as shown at 20.

Arranged in the bottom portion of the gas plating chamber 10 is an article such as a pattern 22 and which is centrally disposed on an electrically heated platen 24. Electrical resistance heaters 25 are suitably positioned on a heat insulating base or slab 26, the latter being composed of asbestos or the like heat-resistant material. Loose heat insulating material 28, such as sand or the like, is arranged about the pattern 22, as shown in FIGURE 1.

In the modified gas plating chamber illustrated in FIG- URE 2, the chamber 30 is provided with a lid or cover hermetically sealed in place. Inlet and outlet opening to the plating chamber is suitably provided as at 32 and 33. The side walls 35 are made of material, such as glass or molded plastic, which is transparent to infra-red heat rays. The article, such as shown at 38, is suitably supported in the chamber and heated by infra-red lamps 40 disposed adjacent the walls of the plating chamber. Infrared rays from the lamps are focused onto the surface of the article to be gas plated, such as shown at 38. In the illustration shown in FIGURE 2, the article is a molded plastic ring. Other substrate shapes and articles may, of course, be used to receive the metal deposit.

In FIGURE 3 a gas plating chamber 49 is illustrated which is mounted on a base or support 42. The plating chamber 49 extends horizontally and is provided with a removable gasket sealed cover or lid 43 at the outer end. An inlet 44 and exhaust outlet 45 are provided for the plating chamber.

Means is provided for rotatably supporting a hollow pattern or cast shape as at 46, the pattern being suitably mounted on a rotatable tubular shaft 48. This shaft 48 extends outwardly through a neck portion 50 and bushing 51 and is rotated by a pulley 55 suitably driven by a V-drive belt from a motor, not shown. A slip ring 57 is arranged on the shaft 48 and is provided with brushes 59 through which electric current is conducted to wire 60 to the electrical resistance heater 62. The latter is provided to heat the pattern or workpiece to be gas plated.

Further, to give specific examples of the gas plating deposits which may be obtained by practicing the inven tion, the following are exemplary.

Example 1 A gaseous mixture comprising 500 ml. of nickel carbonyl, approximately 1500 ml. of carbon monoxide, and 3 ml. of diborane (B H gas) is passed into a plating chamber at the rate of 2000 ml. per minute and brought in contact with a metal pattern While the latter is maintained at a temperature of 350 F. After 3 hours of gas plating, the metal deposited on the pattern surface was found to comprise 0.07% boron and the balance nickel. The nickelboron alloy deposit had a hardness of 50-55 Rockwell C and tensile strength of 190,000 p.s.i.

Example 2 A nickel-boron alloy is deposited on a substrate surface coated wtih graphite, and using the gaseous mixture as described in Example 1. After 3 hours gas plating a metal deposit of 0.020 inch in thickness was produced. Thereafter the diborane gas was discontinued and a deposit of virgin nickel deposited to a thickness of inch to provide a composite deposit consisting of a layer of hard, very strong nickel-boron alloy backed by a heavy layer of relatively soft nickel metal. When the deposited composite shell was stripped from the substrate surface or pattern, the critical surface is constituted of the hard, strong wearresistant metal with a backing of shock-resistant ductile pure nickel having a tensile strength of 80,000 p.s.i.

Example 3 A ring formed of thermosetting resin and having numerals molded thereon is cleaned to remove foreign matter and supported in a gas plating chamber which is evacuated of air to provide a vacuum chamber. A gaseous plating mixture flowing at the approximate rate of 75 ml./minute is passed to the plating chamber while maintaining the vacuum by means of a vacuum pump. The gaseous plating mixture consisted of 25 ml. of gaseous cobalt carbonyl, 50 ml. of carbon monoxide and 1 ml. of diborane. The ring is heated to 350 F. by infra-red heat lamps. A coating of tough cobalt-boron alloy metal is deposited on the heated ring member.

Example 4 A bellows of iron-boron alloy is made by gas plating a form cast in a low melting alloy (M.P. 525 F.), the cast form having a cylindrical cavity as in Example 1, and in which is positioned an electrical heating element. After placing the cast form in a chamber evacuated of air, a gaseous plating mixture is passed into the plating chamber at the rate of 1200 ml./ minute. The plating mixture consisted of 1000 ml. of carbon dioxide; ml. of carbon monoxide; 100 ml. of gaseous iron pentacarbonyl; and 1 ml. of diborane. The casting is heated to 400 F. and after gas plating for about four hours an iron-boron alloy coating of 0.02 of an inch is deposited on the casting to give it a tough, high tensile strength outer shell.

Example 5 A sheet of steel is gas plated as described in Example 1 to give it a coating of wear-resistant metal by gas plating wherein gaseous thermally decomposable boron hydride (B H is substituted for diborane as used in Example 1.

Other boron compounds which thermally decompose to release boron may be used as the boron supplying agent, for example, tetraborane or pentaborane. These boron hyrides (as well as diborane and others) are unstable at room temperature but decompose at this temperature to polymeric higher boron hydrides and hydrogens. Normally, the boron hydrides decompose to metallic boron only above 300 C. or 500 0., according to what authority one is quoting.

The foregoing describes the invention and its application by way of certain specific examples and materials, but it will be understood by those skilled in the art that various substitutions and changes may be made within the broad scope of this disclosure, the invention being more particularly defined in the appended claims.

What is claimed is:

1. A method of producing hard metal coatings composed of boron and other metals by gas plating which comprises bringing a gaseous mixture comprising a heatdecomposable boron hydride selected from the group consisting of boranes, diboranes, tetraboranes and pentaboranes and a heat-decomposable carbonyl of a metal selected from the metals of Groups VI-b, VII-b and VIII of the Periodic Table of elements, in contact with a metal substrate heated to a temperature at which said gaseous mixture decomposes to form metals and produce on said substrate a deposit of a mixture of boron and said metal selected from Groups VIb, VII-b and VIII, said coating of mixed metals being wear resistant.

2. A method as set forth in claim 1, wherein the mixture is diborane and nickel carbonyl.

3. A method as set forth in claim 1, wherein the mixture is nickel carbonyl and diborane, the said diborane con taining impurities of higher boranes that amount to less than one-quarter of its volume.

References Cited UNITED STATES PATENTS 1,987,576 1/1935 Moers 117-106 X 2,494,267 1/1950 Schlesinger et al 148-6.35 2,528,454 10/1950 Schlesinger et al. 117-106 X 2,701,216 2/1955 Seiler 117-106 X 2,849,336 8/1958 Reid et al. 117106 3,018,194 1/1962 Norman et a1 l17107.2

OTHER REFERENCES Powell: Materials in Design Engineering, January 1960, vol. 1, #1, pp. 98-101.

RALPH S. KENDALL, Primary Examiner.

ALFRED L. LEAVITT, Examiner. 

1. A METHOD OF PRODUCING HARD METAL KCOATINGS COMPOSED OF BORON AND OTHER METALS BY GAS PLATING WHICH COMPRISES BRINGING A GASEOUS MIXTURE COMPRISING A HEATDECOMPOSABLE BORON HYDRIDE SELECTED FROM THE GROUP CONSISTING OF BORANES, DIBORANES, TETARBORANES AND PENTABORANES AND A HEAT-DECOMPOSABLE CARBONYL OF A METAL SELECTED FROM THE METALS OF GROUPS VI-B,VII-B AND VIII OF THE PERIODIC TABLE OF ELEMENTS, IN CONTACT WITH A METAL SUBSTRATE HEATED TO A TEMPERATURE AT WHICH SAID GASEOUS MIXTURE DECOMPOSES TO FORM METALS AND PRODUCE ON SAID SUBSTRATE A DEPOSIT OF A MIXTURE OF BORON AND SAID METAL SELECTED FROM GROUPS VI-B, VII-B AND VIII, SAID COATING OF MIXED METALS BEING WEAR RESISTANT. 